Heat Exchangers: Fundamentals and Design AnalysisProf. Prasanta Kumar Das

Department of Mechanical EngineeringIndian Institute of Technology, Kharagpur

Lecture - 02Applications of Heat Exchangers

Hello everyone, welcome back to the second class of Heat Exchangers; Fundamentals

and Design Analysis. In the first class, we have got some idea regarding heat exchangers

and we also try to see that how the concept of heat exchanger evolved in the very don of

civilization when people have invented fire and started learning cooking. So, that is what

we have seen and then of course, over the years, there have been lot of change and heat

exchanger has now become such a important industrial equipment so, we will see more

of it

In this present lecture we want to see the application of heat exchanger. We have to

understand; why we should study heat exchanger, what is its importance and that is why

I like to give some application of heat exchanger to you and then we probably towards

the end of this particular lecture, we will try to see how heat exchangers can be

classified.

(Refer Slide Time: 01:29)

Heat exchangers some different purposes, but if I see that what are the main purposes

served by heat exchanger, first point is control of temperature for process requirement

and product quality. Let me explain it little bit, it is like this that temperature control is

important for many cases; for the for that matter where I am delivering this lecture, this

room is air conditioned. So, in this room, the temperature of the room is maintained

within certain level so that the person who will be occupying this room, they will feel

comfortable.

So, due to some sort of a process, we have to maintain the temperature this way.

Similarly, suppose we are making some sort of metallurgical product and either it has to

be heated or cooled because we need certain attribute of the product; certain property of

the product. So, temperature control is very important and heat exchanger often plays a

very important role in controlling temperature.

Then comes conservation of energy; in these also, the conversion of energy should be

included that when we have some sort of energy conversion process. So, then heat

exchanger is; essential examples are many, but if we think of that; how we are generating

most of the power? Most of the power in this in the modern age, it is being generated

from fossil fuel source; that means, the chemical energy is converted into thermal energy

and then from the thermal energy, we are getting mechanical energy or electrical energy.

So, the chemical energy that is getting converted into thermal energy, some sort of

combustion process is involved and we will see at each and every state, we have got

number of heat exchangers, if we think of a power plant, I mean how many different

varieties of heat exchangers you can you can expect to see? It is better to give some time

and think that how many different varieties of heat exchanger you may expect in a power

plant.

Then protection of environment; actually these 2 point goes hand in hand. Conversion of

energy; in certain cases, it is essential to use a heat exchanger, but during the conversion,

what we do? We waste a good amount of thermal energy and we waste also energy in

different form using heat exchanger. These can be reduced, these wastes can be reduced

and reduction of any waste is a gain. So, when we are stopping the waste or reducing the

waste of thermal energy, what we are doing?

We are protecting the environment, apart from that; there are direct action by which

environment can be protected and; obviously, heat exchanger plays a very important role.

The 3 point which I have told they may not cover all the aspects why heat exchanger is

to be used, but they give some main aspect why heat exchanger or rather what is the

purpose of heat exchange using heat exchanger.

Accordingly, the application of heat exchanger can be identified in 3 broad categories.

Again, there could be controversy, people may say that there are other areas, but what we

think are important that is in the industrial sector; that is the main use of heat exchanger,

many varieties of heat exchanger will be used and then health services; there will be

large number of heat exchangers and in domestic obviously, in our day to day life, we

need heat exchanger for our comfort for some unique processing for our survival. So, we

need heat exchanger; obviously, when I talk survival, the room heating the importance of

room heating in cold countries, in arctic region, nobody can deny.

So, it is not some sort of a luxury, it becomes then the essential step for surviving; one

essential step for surviving. So, heat exchanger plays that important role in each of these

categories. Again there are different types of heat exchanger and we will see slowly;

what are the different types of heat exchangers, etcetera.

(Refer Slide Time: 06:52)

So, let us get familiarised with different demands and the different kind of heat

exchanger which can meet the demand. Industrial application; already I have mentioned

power generation. This could be fossil fuel power like your coal or oil or it could be

nuclear, it could be renewable, whatever may it be, there will be a large number of ferry

unique heat exchangers.

Refrigeration, air conditioning and cryogenics, notionally, they indicate generation of

load temperature. So, in all these cases, we need to have heat exchanger of various

designs. In fact, some sort of a cryogenic plant, the performance of cryogenics plant, the

energy utilisation in a cryogenic plant is so much dependent on heat exchanger that I

mean, a plant cannot be designed properly or rather cannot operate properly, unless we

have designed and selected heat exchangers correctly and operated them very efficiently.

Petroleum refinery, petrochemicals, chemical process industries, again, these are the

main places where number of heat exchangers are used. Very unique heat exchangers are

used, some of the heat exchangers which has been evolved for this type of process

requirement only. So, again this is one important user of heat exchangers.

Metallurgy and material processing; I have already mentioned that some sort of material

property that we can get only by some temperature control. So, again cooling is very

important, sometimes, heating is very important and that can be done with the help of

heat exchangers.

Electronic component cooling; these are again cursorily, I have mentioned somewhere,

but this has become very very important. The next generation of computational power we

can acquire these only by a good thermal management of the electronic components and

that can be done with the help of heat exchangers. Efficient heat exchangers, compact

heat exchangers and obviously, the cost should also be low. The maintainability should

be high and all the other aspects which one can expect from a good industrial

component.

So, electronic component cooling are needed not only for computation, but also for other

purposes and for that; good heat exchangers are needed.

(Refer Slide Time: 09:40)

There are many other topics which we can mention under the industrial application of

heat exchanger, but here I like to impress upon you by showing the vastness of heat

exchanger the range which it covers. So, this range could be many; that means, the

temperature range, it could it covers; there could be from cryogenic temperature to very

high temperature and the size, it covers the material range, it covers starting from

graphite or ceramic to paper, but here I just like to impress upon you regarding the size it

covers.

So, on the left hand side, there is a chemical sample cooler, you can see the dimension of

most important dimensions have been given here, all are in the range of inch, etcetera.

So, you can imagine that what could be the size of a sample cooler which is nothing, but

a heat exchanger on the right hand side ok, left hand side, the heat exchanger is there;

that is an indirect contact heat exchanger may be 2 liquids or a gas and a liquid are the

component, here on the right hand side, we have got a hybrid cooling tower.

Now, in a power plant, the most visible thing from a distance is its chimney, but probably

the next visible thing are the row of cooling tower which are there in a power plant

which are essential to a power plant. So, why it is so prominent because of its size so that

you can have some idea; so, here what is shown; a hybrid cooling tower which is a

combination of force draft and induced draft sorry force draft and natural draft.

So, what one can find. So, this is actually is not a finished one um. So, here there number

of fans will come and this height, this chimney height provide some sort of natural draft

this is not finished one, but you can see the size comparing though no dimension has

been given, but here some people and cars are visible. So, you can see, you can have

some imagine some imagination that what could be the size of this heat exchanger. So,

there is so much of variation in size of a heat exchanger; very small to very big so;

obviously, you can understand; that what is the challenge in designing or analysing this

kind of heat exchanger.

So, left hand side, we are seeing one very small indirect type heat exchanger, right hand

side, we are seeing a very large heat exchanger which is a direct contact type heat

exchanger and construction material, left hand side, if you see it is metal, right hand side,

it is concrete and again we will see that this cooling tower; if we discuss, if we get time

to discuss all these things, we will be find that it depends or it is a combined equipment

for heat transfer and mass transfer. So, there are many things which are very important

and at the same time interesting in the discussion of heat exchanger.

(Refer Slide Time: 13:20)

Health service application; there could be many things, I have just name a few heart lung

machine for cardiac surgery for dialysis the system mechanical system which is used that

needs heat exchanger preservation of cell, tissues, bloods, etcetera, we have to create low

temperature without heat exchanger that is not possible, then ICU; ICU we have to

maintain some sort of a condition; temperature condition is very important and then

incubator premature babies are born, before they are scheduled data date of birth, these

babies are to be nurtured in some artificial environment in some built climate and for that

there are incubator temperature control is very important continuous monitoring of

temperature is very important. So, heat exchanger placing important role, then for

treatment.

So, these are some sort of peripheral thing, but let us think of some treatment let us say

hyperthermia; hyperthermia sorry hyperthermia; hyperthermia is a method of cancer

treatment, treatment of tumour, cancer, etcetera and they are we need high temperature

and; obviously, in the total mechanical system, we have got heat exchanger and then

cryosurgery, here by ultra low temperature, we are doing some certain surgery, bloodless

surgery, etcetera and here also, we need heat exchanger to have this kind of a system.

(Refer Slide Time: 15:08)

Just one example I have shown here, this is the circuit for cardiopulmonary bypass

surgery and you can see that there are different component, but there is one heat

exchanger, there is one heat exchanger, there is one heat exchanger over here and

actually the blood is to be heated or cooled depending on because this is how the body

temperature of the patient that can be also control and that is why we need a very good

heat exchanger; these are unique kind of heat exchanger which are used.

So, I can I can remind the engineers who are involved in the design of heat exchanger the

great responsibility which lies on their shoulder. So, starting from industrial requirement

where we have to be really cautious that we should not waste the precious energy which

we are getting from fossil fuel. We should not degrade the environment in which we are

living and to the life of a patient that is also dependent on heat exchanger and so, how it

should be design. So, that it can cater to the need, it can satisfy the need of such a

varying nature, it can be maintained properly, it can be of low cost, it can be of high

reliability.

So, all these are attributes and when these kinds of variety of applications are there, then

you can understand the challenge.

(Refer Slide Time: 16:56)

So, let us proceed in domestic application, of course, compared to industrial need of heat

exchanger that is less, but that is not less important. So, comfort and at some point, I

have told that that is also some sort of life saving device in cold countries or very hot

countries. So, the human comfort or human liveability has to be has to be satisfied that

we do by air conditioning room heating, basically has AC and lot of heat exchangers

have to be used.

Then cooking and food preservation, it is difficult to get household where there is I mean

there is no refrigerator so; obviously, we have to have heat exchangers in the refrigerator

and design or analysis of heat exchanger is very important one cooking device is shown

in this diagram this is a double steamer.

So, basically what we do for cooking certain food? We need uniform temperature and we

need some control temperature. So, it cannot be put on direct flame. So, here we can see

there are 2 pots. In the external pot; outer pot, there is water, water will boil and it will

maintain a certain temperature. Let us say, it will maintain 100 degree Celsius, then the

food can that will be inside surrounded by this boiling water. So, food can will have lot

of again a liquid, etcetera. So, basically this is heat transfer between 2 liquids through

this wall. So, this is kind of a special indirect heat exchanger. So, you can understand;

how versatile is this component that is heat exchanger.

(Refer Slide Time: 18:57)

Let me give some example from biological domain. Thermoregulation is one of the

prime requirements of higher animals; higher animal, higher animals; they try to

maintain the same temperature of the body, irrespective of our level of activity because

we know that for higher level of activity, we need higher amount of metabolic energy

production, if metabolic energy production is high, then the heat which has to be

dissipated from the body that should also be high, but the heat which has to be dissipated

from the body that does not depends only on the organism or slowly on the living being.

But also it depends on the environment condition because q is proportional to delta t and

this environment condition environmental condition environmental temperature,

particularly, it varies a lot think of a desert region where easily the temperature could be

close to 50 degree Celsius to the arctic region, where it is several degrees below the

freezing point and a human being has to maintain a constant temperature constant body

temperature in all these climate.

So, how it is done? They are very large number of there are very large number of

mechanisms, there are some main mechanisms of course, and there are other minor

mechanisms, basically, using these mechanisms, not only human beings, higher animals,

mammals, etcetera, they maintain their body temperature. Many a time, our body is

compared to a heat engine, but often it is not told that our body is a perfect thermostat.

So, to make it function as a perfect thermostat which will which will which will operate,

keep the body as a complete, I mean constant temperature, many mechanisms are there

like sweating, etcetera and this is not the place to discuss all these thing.

But counter current heat exchange as it is done in heat exchanger that is also one of the

principal, this is usually done by exchanging heat between arterial and venous blood

flowing in opposite direction with a temperature difference and this bloods they passes

through tubular type of structure. So, 2 streams are there and these streams are having

temperature difference, but the nature has understood in its own way that if they flow in

opposite direction, large amount of heat or can be transfer or heat can be transferred in

more effective way.

So, there are many examples. There are examples for cold weather; there are examples

for hot weather.

(Refer Slide Time: 22:15)

So, let me give one example reindeers; they are in the arctic region, they are acclimatized

to withstand cold temperature, low temperature, but suppose there is some sort of ahot

condition in which they have to survive. Now when the outside temperature is high or

your body is generating more heat due to some sort of action. So, what happens; the

brain that is very vulnerable, because the temperature of the brain it should be

maintained and it should be maintained slightly below the other temperature; several

degrees below the other temperature of the body.

So, what is done here? The you can see this is the arterial blood which is coming, it will

also go to the brain and it is going to the brain and this is the venous blood which is

returning back. Now when it is returning back, part of it, it goes through the nasal region

of the reindeer where there is cooling of blood due to some sort of respiratory effect. So,

this cold blood that is taking here which is called carotid rete in the that is basically a

typical structure where the hot blood will be inside and there will be very small number

of vessels cold blood will be passing through this.

So, the blood; hot blood before going to the brain, it will get cooled and the principle is

exactly similar 2 things are there, it is similar to counter current heat exchanger and

again, as I have told that compact heat exchanger here large number of vessels are there

to increase the exchange area. So, the concept of compact heat exchanger, it not only

came to the fertile brain of human being, it is also some invention of nature from its own

experience. So, this is for cooling the blood, sometimes, for heating the blood, this is

needed. So, there are many bloods who are in the arctic region and their leg has to be

protected from frostbite.

So, there the blood is to be heated, not to be cooled or the body part is to be heated and

that is done again by similar type of arrangement by counter current heat exchanger

between the 2 streams of blood.

(Refer Slide Time: 25:06)

Now we go to the classification of heat exchanger. This again, I have taken. I have

mentioned here in the source that I have taken it from the design of R. K. Shah sorry;

from the book Fundamentals of Heat Exchanger design by R. K. Shah and R. K. Shah

and P Sekulic. This is one of the very important book time to time, we will refer this

book and this reference has also been given for the course as a textbook.

Now, the classification can be done based on different categories. So, classification

according to transfer process is one important way of classification and this is what we

like to show here let us say. So, classification according to transfer process; this is very

important. So, this is transfer process; how the heat transfer is taking place based on that

we are doing the classification.

So, first one is indirect transfer; indirect contact type; that means, the 2 streams; they are

not touching each other ok. They are not mixing with each other and most of the heat

exchanger are of this category. Already I have mentioned it. So, what could be the

different heat exchanger in this category? Direct transfer type; that means, single phase

and multiphase. Multiphase means where your boiling or condensation will take place

and storage type; what is direct transfer type? Directly from one stream to another

stream, it is getting transferred; of course, in between, there is a solid phase solid wall.

So, this is direct transfer. So, there is no storage of heat and it could be single phase; that

means, 2 fluids; they are in the either both of them; they are not changing, their phase or

one of them or in some very rare situation, both of them are changing their phase. So,

condensation boiling etcetera that is your multiphase.

Then storage type; so, this also I have explained that one stream is giving thermal energy

to some sort of a intermediate medium where temporarily thermal energy is getting

stored and then that stored energy is transferred to the another fluid. So, that is your

storage type then your fluidised bed. So, fluidised bed probably next class I will show

some figure of this heat exchanger. So, there will be particulate solid and particulate

solid through particulate solid gas is passing.

So, there will be certain amount of energy exchange between the particulate solid and the

gas and again from the particulate solid to another fluid, which will pass through some

sort of a tube. So, this is a typical kind of heat exchanger, but in none of these cases, 2

heat exchanging 2 heat exchanging fluids are mixing with each other. So, this is your

indirect contact type.

Then we have got direct contact type where the where the 2 fluid streams are coming in

contact with each other. There are limitations not all the heat exchanger can be designed

like this, if there are 2 liquid streams which are invisible, we can go for direct contact

type of heat exchanger, if gas one of them is gas and another is liquid, we can go for

direct contact type heat exchanger and let us say liquid and vapour let us say steam and

water we want to exchange heat between them. So, we can have again direct contact type

of heat exchanger. So, these are the three possibilities in general where we can have

direct contact type heat exchanger.

So, there are very important heat exchanger in this category; though less in number, in

power generation and in other places, we will find that there are direct contact type heat

exchanger and for their obvious advantage, we use direct contact type heat exchanger,

there are other classification, we will take of them in our next class and a from this

classification also, we will try to elaborate certain thing in our next class up to this. Let

us have for the present class, again I will request you, if you have got any queries, please

interact in the forum and we will try to clarify it.